Liquid electrophotographic toners

Abstract

Liquid toners are generally recognized as being capable of providing sharper electrophotographic images, but have been found to provide less than desirable results in multicolor imaging processes. The selection of a unique combination of (a) the ratio of conductivities between the toner liquid and the total toner composition, and (b) the zeta potential of the toner particles in the carrier liquid have been found to provide unique benefits to the quality of the liquid tone multicolor images.

What is claimed is: 
     
       1. An electrophotographic process for producing high quality full color prints wherein color separation toner images are assembled on a positively charged photoreceptor using successive liquid toning steps, comprising selecting two or more liquid toners comprising toner particles comprising a pigment particle having polymer particles on its exterior surface, said polymer particles having charge coordinating moieties extending from the surface of said polymeric particles, said toner particles being dispersed in a non-polar carrier liquid, said two or more liquid toners having (a) a ratio of conductivities of said carrier liquid in said liquid toner and of said liquid toner less than 0.6, and   (b) a zeta potential of said toner particles between +60 mV and +200 mV, and carrying out the assembly of said color separation toner images on said photoreceptor using said successive liquid toning steps.   
     
     
       2. An electrophotographic process for producing high quality full color prints wherein color separation toner images are assembled on a positively charged photoreceptor using successive liquid toning steps, comprising selecting two or more liquid toners comprising toner particles comprising a pigment particle having polymer particles on its exterior surface, said polymer particles having charge coordinating moieties extending from the surface of said polymeric particles, said toner particles being dispersed in a non-polar carrier liquid, said two or more liquid toners having (a) a ratio of conductivities of said carrier liquid in said liquid toner and of said liquid toner less than 0.4, and   (b) a zeta potential of said toner particles between +60 mV and +200 mV, and carrying out the assembly of said color separation toner images on said photoreceptor using said successive liquid toning steps.   
     
     
       3. An electrophotographic process as recited in claim 2 wherein said ratio of conductivities is less than 0.3. 
     
     
       4. An electrophotographic process for producing high quality full color prints wherein color separation toner images are assembled on a positively charged photoreceptor using successive liquid toning steps, comprising selecting two or more liquid toners comprising toner particles comprising a pigment particle having polymer particles on its exterior surface, said polymer particles having charge coordinating moieties extending from the surface of said polymeric particles, said toner particles being dispersed in a non-polar carrier liquid, said two or more liquid toners having (a) a ratio of conductivities of said carrier liquid in said liquid toner and of said liquid toner less than 0.6,   (b) a zeta potential of said toner particles between +60 mV and +200 mV, and carrying out the assembly of said color separation toner images on said photoreceptor using said successive liquid toning steps, and   (c) the property that a continuous film is formed on those areas of the photoreceptor where said liquid toner is deposited said film being formed at a temperature less than 25° C. and in a time after deposition of less than 20 seconds.   
     
     
       5. An electrophotographic process as recited in claim 2 further characterized as having (c) the property that a continuous film is formed on those areas of the photoreceptor where said liquid toner is deposited said film being formed at a temperature less than 25° C. and in a time after deposition of less than 20 seconds. 
     
     
       6. An electrophotographic process as recited in claim 3 further characterized as having (c) the property that a continuous film is formed on those areas of the photoreceptor where said liquid toner is deposited said film being formed at a temperature less than 25° C. and in a time after deposition of less than 20 seconds. 
     
     
       7. An electrophotographic process as recited in claim 1 further characterized as having (c) toner particles comprising at least one component selected from resins and polymers having a Tg less than 25° C. 
     
     
       8. An electrophotographic process as recited in claim 2 further characterized as having (c) toner particles comprising at least one component selected from resins and polymers having a Tg less than 25° C. 
     
     
       9. An electrophotographic process as recited in claim 3 further characterized as having (c) toner particles comprising at least one component selected from resins and polymers having a Tg less than 25° C. 
     
     
       10. The electrophotographic process of claim 7 wherein the Tg is less than -10° C. 
     
     
       11. The electrophotographic process as in claim 1 further comprising transferring said assembly of said color separation toner images to a receptor in at least one step without loss in color and sharpness. 
     
     
       12. An electrophotographic process for producing high quality full color prints wherein color separation toner images are assembled on a positively charged photoreceptor using successive liquid toning steps, comprising selecting two or more liquid toners comprising toner particles comprising a pigment particle having polymer particles on its exterior surface, said polymer particles having charge coordinating moieties extending from the surface of said polymeric particles, said toner particles being dispersed in a non-polar carrier liquid, said two or more liquid toners having (a) a substantially monodispersed toner particle size of average diameter between 0.1 and 1.5 microns,   (b) a zeta potential of said toner particles between +60 mV and +200 mV,   (c) a ratio of conductivities of said carrier liquid in said liquid toner and of said liquid toner less than 0.6,   (d) a conductivity of said liquid toner in the range 0.10×10 -11  and 2.0×10 -11  mho.cm -1 , and   (e) toner particles comprising at least one component selected from resins and polymers having a Tg less than 25° C.   
     
     
       13. A liquid toner for use in developing electrophotographic images of at least two assembled toner layers on a charged photoreceptor, comprising toner particles comprising a pigment particle having polymer particles on its exterior surface, said polymer particles having charge coordinating moieties extending from the surface of said polymeric particles, said toner particles being dispersed in a non-polar carrier liquid, said liquid toner having (a) a substantially monodispersed organic polymeric particle size of average diameter between 0.1 and 1.5 microns,   (b) a zeta potential of said toner particles between +60 mV and +200 mV,   (c) a ratio of conductivities of said carrier liquid in said liquid toner to said liquid toner of less than 0.6, and   (d) a conductivity of said liquid toner in the range 0.10×10 -11  and 2.0×10 -11  mho.cm -1 ,   said liquid toner being capable of a continuous film on a photoreceptor where said liquid toner is deposited, said film being formed at a temperature less than 25° C. and in a time after deposition of less than 20 seconds, at a coating thickness of about 0.30 microns.   
     
     
       14. An electrophotographic process for producing high quality full color prints wherein color separation toner images are assembled on a positively charged photoreceptor using successive liquid toning steps, comprising selecting two or more liquid toners each comprising charge carrying toner particles comprising a pigment particle having polymer particles on its exterior surface, said polymer particles having charge coordinating moieties extending from the surface of said polymeric particles, said toner particles being organosol particles surrounding a pigment particle dispersed in a non-polar carrier liquid, said two or more liquid toners having (a) a ratio of conductivities of said carrier liquid in said liquid toner and of said liquid toner less than 0.6, and   (b) a zeta potential of said toner particles between +60 mV and +200 mV, and carrying out the assembly of said color separation toner images on said photoreceptor using said successive liquid toning steps.   
     
     
       15. An electrophotographic process for producing high quality full color prints wherein color separation toner images are assembled on a positively charged photoreceptor using successive liquid toning steps, comprising selecting two or more liquid toners each comprising toner particles comprising organosol particles surrounding a pigment particle and having chelating moieties attached thereto, said toner particles being dispersed in a non-polar carrier liquid, said two or more liquid toners each having (a) a ratio of conductivities of said carrier liquid in said liquid toner and of said liquid toner less than 0.6, and   (b) a zeta potential of said toner particles between +60 mV and +200 mV, and carrying out the assembly of said color separation toner images on said photoreceptor using said successive liquid toning steps.   
     
     
       16. An electrophotographic process as recited in claim 15 further characterized as having (c) the property that a continuous film is formed on those areas of the photoreceptor where said liquid toner is deposited said film is formed at a temperature less than 25° C. and in a time after deposition of less than 20 seconds. 
     
     
       17. An electrophotographic process as recited in claim 14 further characterized as having (c) the property that a continuous film is formed on those areas of the photoreceptor where said liquid toner is deposited said film is formed at a temperature less than 25° C. and in a time after deposition of less than 20 seconds. 
     
     
       18. An electrophotographic process as recited in claim 14 further characterized as having (c) toner particles comprising at least one component selected from resins and polymers having a Tg less than 25° C. 
     
     
       19. An electrophotographic process as recited in claim 15 further characterized as having (c) toner particles comprising at least one component selected from resins and polymers having a Tg less than 25° C. 
     
     
       20. An electrophotographic process as recited in claim 16 further characterized as having (c) toner particles comprising at least one component selected from resins and polymers having a Tg less than 25° C.